This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

Medieval Danse Macabre Fresco in Northern Brittany.

A Belgian self-built tower inspired by the Bible and ancient civilizations.

The largest medical and anatomical collection in France lies hidden from the public.

Notorious artist squat renovated into legal studios.

The headless bodies of more than 1,300 guillotined victims of the Reign of Terror are buried here in mass graves.

Weird wax anatomical models reside here, as do other anatomical specimens.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

The personal library of the founder of modern neurology is open to visitors.

Paris' fabled purveyor of exotic taxidermy and natural history curios.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

A haunting collection of the vanished and disappearing natural world.